Communication system



June 26, 1945- L. EsPENscHlED COMMUNICATION SYSTEM 7 Sheets-'Sheet'lFiled Oct. 9, 1942 .n /ER MIL .m u n 6 w B d 5 7 9mm Y 5mwv U ,m m m m.i 2. 4., .o

lJune 26,1945. EsPENsCHlED l l2,379,221

'COMMUNICATION SYSTEM FiledV oct. 9, '1942; v 7 sheets-sheet 2 FIG. 2

PRIMARY DEAN SIYI TCH /Nl/ENTOR ByL. ESPENSCH/El June 26, 1945. L.EsPENscHxED COMMUNICATION SYSTEM Fil-ed oct. 9, 1942A '7 Sheets-Sheet 3SECONUR? BEAM SW! TCH i me. E SPENS CHIED A t tbe/mc June Z6, 1945. L.EsPENscHlED COMMUNICATION SYSTEM '7 Sheets-Sheet 4 Filed OCI'.. 9, '1942START BV A Tron/MEV June 26, 1945.

| EsPENscHIED 2,379,221

COMMUNICATION SYSTEM 'Filed oct.f.9, 1942 v sheets-sheet e Patented June26, 1945 2,379,221 COMMUNICTIQN SYSTEM Lloyd Espenschled, Kew Gardens,N. Y., assigner to Bell Telephone Laboratories, Incorporated,

New York, N. Y., a corporation of New York ApplicationOctober 9, i942,Serial No. 461,439

19 Glas.

This invention relates to electrical switching methods and switchingdevices and particularly to these methods and devices when applied tocommunication systems and to signaling systems in general.

The objects ofthe invention are to simplify the devices used yto performthe switching of communication lines and other electrical circuits; toeliminate to a large extent the moving mechanisms heretofore used forthis purpose; to reduce the number. of switching stages necessary forthe establishment of connections between telephone or other lines; toincrease the speed with which -connectionsmay be established; and inother respects to obtain improvements in switching methcds and devices.Many varieties of automatic switching mechanisms have been proposed inthe past for interconnecting the lines of telephone, telegraph, andother communication systems. In most all cases these prior mechanismshave depended largely upon the use of electromechanical devices in whichmoving parts serve to perform the selective and connecting operationsinvolved in the establishment of the desired connections. While some ofthese types have been developed to a high degree oi reliability, it istrue nevertheless that the presence of moving mechanical elementsimposes limitations on the speed of operation and also introduces otherproblems. Also there.have been a number of suggestions heretofore forthe `use of the cathode beam tube for selecting telephone lines andother'similar circuits. Furthermore, it

has been previously suggested to use cathode.

beam tubes as distributors in systems of the usual multiplexdistribution type.

En accordance with the present invention improvements and advantages areobtained over these prior devices by means of a switching system inwhich electrical connection may be estabiished between any two lines ina group, suchas the calling and called lines in a telephone oice,

the medium of the beams once for each scanning cycle. The system isprovided, however, with means for varying the relation of the twoscanning beams in accordance with information receivedconcerning theconnection that isvdesired. When, therefore, it is desired to establisha connection between any calling line and any called line, the relationbetween the two beams is varied by an amount corresponding to theidentity of these lines, so that each time the rst beam engages thecalling line the second beam simultaneously engages the called line.rrhus the calling and called lines are connected together once percycle, and the scanning rate is so rapid that a substantially continuousconnection is maintained.

Another and related feature of the invention is a system in which `thelines in the incoming scanning field and the lines in the outgoingscanning eld constitute two separate groups of lines or trunks. `Forexample, the outgoing lines may be a group of trunk circuits over whichcalls are extended from the incoming lines or trunks. By subdividing theoutgoing-lines into subgroups it is possible to choose any one of anumber of differy ent directions for routing the incoming calls.

Another feature oi the invention is a scanning system in which theelements in the scanning elds are variably energized in accordance withthe current variations infthe lines produced by the speech orcommunication signals therein, and these variable energiaations are.communicated from one line to another by means of the interveningelectron beams.

through the medium of scanning devices. More speciiically a group oflines, having an appearance in a scanning iield as calling or incominglines, are scanned repeatedly and at high speed by an electron beam,such as that produced by a cathode beam tube, and at the same time thesaid group of lines, having another appearance in a second scanning eldas called jor outgoing lines, are scanned repeatedly by .a secondelectron beam. Normally these twobeams are in synchronism and in phasesuch that each line in the incoming field is electrically connected tothe corresponding line in the outgoingiield through Another feature ofthe invention is a system in A which the designations of the lines orother circuits to be connected for conversation through the scanningbeams are utilized to introduce a phase displacement between said beams,so that said beams engage the ,calling and called lines simultaneouslyeach time they pass through a scanning cycle.

iiiuotlier feature of the invention is a system in which the scanningdevices are driven synchronously from a common source of high frequencycurremt and in which the designations ofany pair of lines or circuits tobe interconnected are used to produce a corresponding shift in the phaseof the current supplied to' drive one of said beam devices, therebyeecting a phase relation between the synchronously moving beams suchthat they engage simultaneously the desired pair of lines or circuits oneach scanning cycle.

Another feature of the invention is a system m which the lines have anappearance 1n a primary i beam scanning device and also have appearancesin each of a plurality of associated secondary beam scanning devices,the beams of all devices being driven synchronously over the linesappearing therein, together with means for introducing denite andvarying phase displacements between the beams of said secondary scanningdevices and the beam or said primary device. so that simultaneouscommunications may take place between any desired number of pairs oi'lines.

These and other features of the invention will be discussed more fullyin the followingr detailed speccation. t In the drawings accompanyingthe specificaion:

Fig. 1 is a conventional diagram illustradns .a telephone systemincorporating the features of the present invention;

Figs. 2 to '27. inclusive, when arranged in the order illustrated in me.il disclose the system of Fig. l in greater detail;

Fig. 2 discloses a primary beam switch in which the subscribers lines'or other circuits appear and also shows two of these lines;

Fis. 3 shows two oi the secondary beam switches in which the subscriberslinea also appear as well as other circuits with which it is desired tomaire connection;

Figs. d and 5 show a pair of designation resisters for registering thenumbers oi calling and called lines respectively;

Fiss. il and 'l' disclose a nation registers; and y Fie. ti is anenlarged fragmentary view illustrating the structure or the beamswitches.

The invention in its broader aspects contemplates a multiplex system inwhich a plurality of communication channels-are established concurrentlyfor voice communication, telegraph signaling or transmission of anyother desired kind. In the present disclosure, however, a telephonesystem has been chosen for the purpose of illusytrating theminvention.It is also assumed that there are one hundred lines in this system, allof which may be subscriberslines if desired or a part of which may betrunks, such as those interconnectins one telephone cnice with another.ln any event it will be obvious that the invention is not limited to anyparticular capacitynor to any particular division 0r disposition of thecircuits comprising this systern.

Referring irst to Fien l, there is illustrated diagrammatically a singleprimary beam switch |00 in which the incoming lines or' a group haveindividual appearances in a circular rowl of electrodes. Two or theselines, those having the designations 30 and "42" are shown in thedrawing. The primary beam switch |00 is connected over a commontransmission medium |l| to a plurality of secondary beam switches |02,III. etc., the number of these secondary switches corre-` sponding tothe number of permissible simultaneous communications. The switches |02and second pair of desis- .|03 are similar in structure to the switchH00,

and thelines appearing in the switch |00 also have the same relativespatial appearance'ln each of the switches |02, |03, etc'. T wosubscribers' lines, No. 62 and No. 20, are shown loutgoing from thevsecondary switches. If it sassumed that the system comprises one hundredsubscribers' lines and that the switches have a capacity for one hundredcircuits, then the entire circumferential row of electrodes in each ofthese switches is occupied by the subscribers lines. In other words,lines numbered "0 to "99" would appear in spasame spatial sequencearound the circumference mon source l l,

of each of the secondary switches |02, |03. etc; However, if it isdesired to include trunks or other circuits incoming from and outgoingto distant points, a portion of the appearances around the circumferenceof the beam switches |00', |02, 03, would be devoted to these incomingand outgoing circuits, and the remainder of the appearances in theseswitches would be devoted to the subscribers lines, which would alsohave the corresponding spatial appearances in the beam switches, One ofthe incoming circuits lili and one of the outgoing circuits il@ areillustrated `in the drawing.

A plurality of designation registers 05, lllt, etc., are provided forregistering the designations of any pair of lines or circuits betweenwhich it is decided to establish a communication connection by way of apair of beam switches. M0, U02. The resister itt comprises two steppingdevices itl and itt which are essentially the same in structure as thewell-known two-motion step-by-step switch used in automatic telephonesystems. The

subscribers lines appear according to their numerical designations inthe terminal banks off the stepping device lill, which operatesautomatically, like a line lnder, to und the terminals oi any line onwhicha calling condition is present. Having found the calling line, thevertical rotary movements perfumed by the stepping de-J vice lill are ameasure or a registration of the tens and units digits ci the line. Aswill be explained hereinafter, these vertical and rotary' movementscause the setting of a pair of variable condensers whichy togethercomprise a phase shifter W0. The other step-by-step device 80d of theregister itil is similar to the finder lill, except that it responds tothe impulses transmitted by the calling subscriber to perform verticaland rotary movements representing the tens and units digits of thecalled line or circuit and in so doing imparts corresponding settings tothe condensers of the phase shifter il 0.

The purpose of the phase shifters tot and titl is to impose a. phaseshift in the voltage taken from the beam-driving source lll which is anexact measure of the spatial separation of the calling and called linesin the primary and secondary beam switches. Thus if the beams H2 and H3,which are' driven in synchronism over their circumferential rows ofelectrodes by the comare in phase with each other, they encountersimultaneously the two appearences of each,0f the successive lines overwhich they move. But by setting the phase Shifters itil and H0 inaccordance with the designations of the calling and called lines it ispossible to shift the phase of the beam H3 with respect to the phase ofbeam ||2 by an amount which corresponds to the spatial distance betweenthe calling and called line appearances in the switches l0@ and M2.Therefore, as the beams rotate in synchronism they encounter thecallingand called lines simultaneously once per revolution.

1n like manner the register |06 comprises a step-by-step line nderdevice H6 having an associated phase shifter I|5 and a stepping deviceHB having an associated phase shifter il?. It will be noted that theregisters |05 and |06 are commontc all of the subscribers lines and areassocated respectively withthe secondary beam switches |02 and |03. Andin likeimanner for each of the remaining secondary beam switchesNYclosed in a sealed vacuum tube. vare arranged on the exterior of thetube in any not disclosed in the drawing a corresponding' register isprovided.

Referring now to Figs. 2 to 7, the subscribers' lines, which are assumedto be numbered from to "99, appear in the central office in individualcontrol and transmission circuits. For

42, is connected by way of conductor 2M to the forty-second anode 200,and line 20|, the number of which is 30, is connected by Way ofconductor 209 to the thirtieth anode 2I0 in the beam switch 206. Thebeam switch 206 includes a central electron-emitting cathode 2H, acollector grid 2| and a set of driving coils 2|3, 2M, 2lb and 2I6. Thecentral cathode, the collector grid and the circumferential anodes areall en- The driving coils convenient manner and serve to set up arotating magnetic field which causes the electron beam 2li (virtual orreal) to rotate at a velocity depending on the frequency of theenergizing source 2id. For a, more complete description of the generalprinciples of the rotating radial beam tube reference is made tothepatent to A. M. Skellett 2,217,774 of October l5, i940.

The primary beam switch 206 is paired with each of a plurality ofsecondary bearnswitches 300, 30|, etc., over a common transmissionconductor 302 which interconnects the collector grid `M2 of the switch20d and the collector grids 303,

5304i, etc., of the secondary beam switches. The beam switch 300 issubstantially the same as lswitch 200; it has a circular row of onehundred anodes spaced and numbered in the same order, a collector grid303, a central' electron-emitting cathode 300 and the collector drivingcoils 06, 307, 000 and 303. In addition the switch 300 is provided witha control grid 3|0, the purpose of which will be explained hereinafter.Likewise the secondary .beam switch 30I comprises a central cathode 3H,a control grid 3I2, a collector grid 343, a circular row of one hundredanodes and driving coils, two of which, 3M and tlf, are illustrated inthe drawings.

When the primary beam switch 206 is paired with the secondary beamswitch 300 for establishing communication betweena pair of subscribersmovable plate 401 of the variable condenser 403 by an amountcorresponding to the vertical movement of the shaft 40|; and the pinion406 serves to set the movable plate 409 of the variable condenser 4I0 byan amount corresponding to the rotary movement of said shaft. The shaft40| takes a number of vertical steps varying from one to ten inaccordance with the tens digit of the calling subscribers line and in sodoing sets the movable condenser plate 407 in any one of ten positionswith respect to the stationary plates 4H, 4|2, 4|3 and 4M. The gearingbetween the plate 401 and the ratchet 405 is such that the plate 40'!lmakes a complete revolution -of 360 degrecs for ten steps of the shaft60|. Therefore, each ofthe successive values of the tens digits isrepresented by an angular rotation of the plate 401 which is a multipleof 36 degrees.

The four stationary plates of the condenser 00 are connected to thecorners of an electrical. bridge comprising resistors M5 and di@ andthe` condensers di? and M8, and the bridge input circuit tis is alsobridged by a resistor d20 having its mid-point connected to ground. Whenan alternating voltage is applied to the input circuit 4| 9, the bridgeapplies potentials to the four quadrant plates 0| I, SI2, 4|3 and dlt toestablish adjacent these plates an electrostatic iield the intensity ofwhich varies in synchronisrn with the f -the patent to L. A. Meacham.2,004,613 of June l1,

In like manner the phase shifter @I0 has ten different positionsrepresenting the ten different values of the units digitl of the callingline, and

' each of these positions of the movable plate 30s is a correspondingmultiple of 36 degrees. The

' stationary'plates 122, #323, Mii and S25 are conlines,`\the relativeposition or phase of the beams ment, step-by-step rider switch. It has abrushcarrying shaft MI which is stepped vertically to select any one often levels of terminals, and which is stepped in a rotary direction toselect any individual set of terminals in the level. The starting,controlling and stepping mechanism 402 is illustrated conventionally andmay be of the usual well-known character. In -addition to the standardvertical and rotary ratchets 403 and 404 by which the brush shaft 40| isdriven vertically and in its rotary directions, the shaft 40E, carriesa' driving ratchet 405 and a driving pinion 406'. The driving ratchet405 serves to adjust the nected to the bridge comprising resistors 26and 421 and condensers M8 and 29 which, together with the groundedresistor l$30, is connected across the input circuit tai. The effect ofthe variable condenser M0 and the associatedA bridge circuits is, likecondenser 300, to shift the phase of 4the voltage in the input circuit@3| by ten equal steps of 36 degrees each through the entire cycle of360 degrees.

If, therefore, the voltage from the beam-driving source 2 I 8 is appliedthrough the phase shifters SII) and 408 in series, the voltage in theoutput circuit 432 will have a phase relative to that of the source 2idwhich has been shifted by a multiple of 36 degrees which is equal tothenumerical sum of the tens and units digits. In other words, the unitsphase shifter would, under this assumption, produce a shift of the samemagnitude as that produced by the tens digit. It is necessary,therefore, to reduce the shift eiected by the units digit to one-tenthof the shift effected by the same tens digit. The necessity for doingthis can best be understoodA by referring for the moment to the beamconnectors. Since there are lines appearing in ten groups of lten aroundlthe 360 degrees of the beam switch, each group grees. The phase shift,therefore, of the beam SI5 over a group of ten lines corresponds to onestep of the tens digit phase shifter 408, namely, a 36-degree shift.However, a shift of the beam 3|6 from one line to the next within agroup of ten corresponds :to one-.tenth of the shift produced by asingle step of the units phase shifter 4I0. Hence in order that thephase shifter 4l0 may produce increments of phase shift of 3.6 degreeseach rather than increments of 36 degrees, a frequency multiplier 433 isinserted between the source 2|8 and .the input circuit 43i of the phaseshifter 4I0. The multiplier 433 multiplies the frequency of the source2l0 ten times. Although the shifter 4l0 shifts the frequency of theinput voltage by steps of 36 degrees, each one of these steps in realitycorresponds to only a 3.6-degreeshift when compared with the originalfrequency. In Ithe output circuit of the phase shifter 4|0 a frequencydivider 434 is in- `serted for the purpose of dividing .the frequency ofthe output voltage by -ten and thus restoring it to the same frequencyas the source 2 I8. Thus, the voltage taken from the source 2id isapplied to the units shifter dit and appears in the output circuit M9displaced in phase by a multiple of 3.6 degrees which is equal to thenumerical value of the units digit of the line which causes the settingof the phase shifter M0. This voite f with the units phase shift thereinis then applied to the tens phase shifter 400 as above explained andappears in the output circuit 432 with an added shift which is equal tothe multiple of 36 degrees corresponding to the numerical value of thetens digit that causes the setting of the phase shifter 408. We have,therefore, in the output circuit 432 a voltage which is displaced inphase, relative to the phase of voltage 2l0, which is an exact measureof the designation of 4the calling subscribers line. An ampliiier 440 isprovided if desired for increasing the energy in the output circuit 432.

The phase displacement of the beam 3|0, however, must taken into accountnot only the number of the calling line but also the number of thecalled line. To lthis end the phase shifting register 500, whichresponds to lthe number of the called line dialed by the callingsubscriber, is provided with a tens digit phase shifter 50i and a unitsdigit phase shifter 502. These phase shifters are identical with thoseshown in Fig. 4; :the shifter 50i comprises a movable plate 503 driventhrough ten Vsuccessive steps by the vertical movement of the shaft 504,together with the stationary plates and associated bridge circuits; andthe shifter 502 comprises the movable plate 505 which is rotated throughten equal steps by the rotary movement o1' the shaft 50S, together withthe four stationary plates and the' associated bridge circuits.

Since the resultant phase shift for the beam of the secondary switchrelative to the phase of the beam of the primary switch is the algebraicsum of the phase shifts representing the calling andqcalled lines, thecalling line phase shifters of Fig. 4 are connected in series with thecalled line phase Shifters of Fig. 5 before the final voltage is appliedto the beam-driving coils of the secondary switches. To this end theoutput circuit 432 from the phase shifter 408 is connected t0 the inputcircuit of the phase shifter 502. As in the case of the phase's'hifter4|0, a frequency multiplier 506 is introducedto multiply thefrequency ofthe voltage in the circuit 432 by ten beforelapplying it to the unitsphase shifter 502.

` angular measure The effects of this multiplication is, as explained,to produce a voltage in the output circuit 501 whichis shifted by unitsof 3.6 degrees each with respect to the phase of the voltage ln thecircuit 432. The voltage in the output circuit 501 is restored to thenormal frequency of the source 2|0 by the frequency divider 505. Thisvoltage is then applied to the tens phase shifter 50| and the resultantvoltage in the output circuit 509 has a phase equal to :the algebraicsum of the phases representing the calling and called lines. A suitableamplifier 5I3 serves to increase the voltage in the output circuit 500.

Since it is the difference between the spatial locations of the callingand called lines in the beam switches that determines the phasediierence necessary to bring the beams onto these lines simultaneouslyas they sweep through their cycles, thephase Shifters of the calling andcalled lines are arranged to produce shifts of the opposite sense. Morespecifically, the phase shifters Mit and tid produce a shift of thenegative sign in the voltage wave, whereas the phase Shifters bei and502 of the called line produce a phase shift of the positive sign. Thisdiference of sense may be obtained by arranging the driving connectionsof the plates 401i and 5th such that they rotate in opposite directionswith respect to the stationary condenser plates and by arranging theshafts 405 and 50G to rotate the movable plates i053 and 505 in oppositedirections. If the number of the calling line is numerically greaterthan the num ber of the called line, the negative phase shift of thesecondary beam caused by the phase-shifting register 000 exceeds thepositive phase shift of the beam caused by the phase-shifting register50o by the difference between the -two numbers, and the negative signbefore the resultant phase shift applied to the secondary beam indicatesthat this beam lags the primary switch beam by the phase angle whichequals the spatial separation between the calling and called lines.However, if the number of the called line is greater than that of thecalling line, the positive phase shift produced by the register' 50@exceeds the negative phase shift produced by the register 406, and thepositive sign before the resultant phase shift apn plied to thesecondary beam indicates that the secondary beam leads the primary beamby the shift produced in accordance with the number of a calling lineand the positive phase shift produced in accordance with the number of acalled line gives a resultant phase shift between the primary andsecondary beams which is an exact of the spatial separation of thelines.

f It will be noted that one of the advantages of multiplying thefrequency by ten before and dividing it by ten after applying thevoltage to the units phase Shifters is the uniformity obtained in thedegree of motion and accuracy required for both the tens and unitsShifters. Ii' desirable, however, it would be possible to obtain thenecessary shift intervals of 3.6 degrees for the units digits withoutchanging the frequency by arranging the movable plates of the unitsShifters to move through distances which areV one tenth of the distancestraversed by the tens Shifters for the same digital values. Also it willbe understood that "where the frequency multipliers and dividers areused they are arranged to preserve the proper relation between phases ofthe voltage Tucker and H. J. Merchant, Post Omce Electrical Engineers'Journal, July 1942, volume 35, Part 2, page 62. However, it will beunderstood the frequency controlling devices used herein may be of anysuitable and desirable type.

When the primary beam switch 205 is paired with the secondary beamswitch 3M for establishing communication between a pair of subscribersnumbers.

lines, the relative position or phase of the beams 2li and Sil iscontrolled by the pair of phaseshifting registers 600 and 700. Thecalling line register 600, like the register v300, is a line-iindingmechanism having access to all of the subscribers lines and includes atens phase shifter ddl and a units phase shifter 602. Likewise, thecalled line register 100 corresponds to register 500 and coniprises atens phase shifter Tdi and a units phase shifter lill. Voltage from thealternating source 2id is applied to shifter W2 through a multiplier B03which multiplies the frequency by ten and the output voltage from theshifter Z, after having its frequency divided by ten by the divider801i, is applied to the phase shifter 50i. The output voltage from theshifter 60H is amplified by amplier E05, following which its frequencyis again multiplied by ten by the multiplier 'm3 and applied to theshifter m2, The output voltage from the shifter 'Q02 is restored to itsoriginal y frequency by the frequency divider ldd and is then applied tothe phase shifter ldl. The voltage output from the shifter mi isamplified by amplifier i053 and is then applied over circuit 'ldd to thequadrature coils sid, dit, etc. of the secondary beam tube 30E.

In like manner other pairs of phase-shifting registers and secondarybeam switches (not shown) are provided, the total number being selectedin accordance with the maximum num ber of conversations to be permitted.

From the foregoing it will be seen that any pair of lines may beconnectedv for communica- I tion through the primary and secondaryswitch beams by utilizing a single source of alternating voltage 2id todrive the primary beam in phase with the voltage from said source and todrive the secondary beam with the necessary phase displacementintroduced. Accordingly, the source 'dit is connected directly to thequadraturecoils .2l3, 2M, 2|5 and 2H; of the primary Switch 26E and isconnected by Way of circuit il@ and the several pairs of phase-shiftingregisters in parallel to the quadrature coils of the correspondingsecondary beam switches. For examplel the circuit 2l@ is connectedthrough the phase Shifters did, 08, 502 and 50i in series, thence overcircuit dd to the quadrature coils of the beam switch 3mi.' Also thecircuit 2id is connected. through the phase Shifters 602, 6M, 102 and'110| and thence over circuit '506 to the quadrature coils of the beamswitch 30|. And in like manner 'the supply circuit 2 l 9 is connectedthrough the phase Shifters of succeeding pairs of phase-shiftingregisters to the quadrature coils of the correspondpaired with the beam2H for a particular conversation, is driven in synchronisni with thevoltage of the source ZIB and with the beam 2li' but with a phasedisplacement which measures the difference between the calling andcalled line And the same is true of the beam dll and of the beams ofother secondary switches not shown in the drawings.

It is, of course, desirable in a communication system, such as the onehere illustrated, that the parties be able to carry on a two-wayconversation.` This facility'is made possible in the present system,notwithstanding the unilateral character of the usual cathode-beam tube,by taking advantage of the well-known phenomenon of secondary electronemission. The space between the collector grid and the ring of anodes ofthe rotary beam tube disclosed herein is capable of conductingA signalsin both directions if the proper relative voltages are selected. -Thecentral cathodes are connected to the negative pole of the battery whichproduces the electron beam, the positive pole of this battery beinggrounded, the anodes are connected respectively through their individualtransmission circuits to ground, and the common collector grid isconnected to the positive pole of a battery of relatively low voltage,which also has its negative pole grounded. For exemple, the rotary beamswitch 206 has its central cathode 2li connected to the negative pole ofbattery 220 and the positive pole of this battery is connected directlyto ground. The individual anodes 200, 2id, etc., are connected throughtheir transmission circuits 20d, 205, etc., to ground;

is connected over the common transmission conductor 302 throughimpedance coil Sid to the positive pole of battery dit. The battery 22dsets up a voltage, say 15G-volts, between the cathode 2M and each anode,which is suicent to cause a beam of electrons to ow from the cathode tothe anode through slits or openings in the collector grid 2&2notwithstanding the positive potential impressed upon the collector gridby the relatively small battery tlg. say l0 volts. lf, while theelectron beam 2li is passing through the collector. grid 2li? to anindividual anode, the potential of the anode is varied in accordancewith the speech signals originated in the line connected to said anode,the intensity of the secondary emission set up by the impingement of thebeam on the anode varies correspondingly and in turn imparts acorresponding variation to the potential'of the collector grid, to whichthe electrons of secondary emission are directed. The variations of grid2li are impressed over the common medium 302 to the collector grid ofthe associated secondary switch, sayA the grid 30e of to impinge uponaparticular anode, and these variations in the beam are reflected bycorresponding potential variations on the anode, which lin turn areimpressed as speech signals upon the called line connected to saidanode. On the other hand, if speech signals are originated in the calledline wl'iichis connected to a particular anode in the beam switch 300,the potential varia- And the collector grid 2&2

cathode 000.

' the associated anode 8c3.

collector grid 303 to which the secondary emission is directed. 'Ihepotential variations of the grid 303 are transmitted over the medium 302to the collector grid 2l2, and the grid 2l2 varies the intensity of thebeam 2li as it passes from the cathode 2li through the grid to theparticular anode with which the calling line is associated. Accordinglythe potential of the anode is varied in accordance with speech signalsand results in the transmission of these signals over the callingsubscribers line. Thus the calling and called subscribers may tall: toeach other in either direction over the established connection, makinguse of the primary and secondary emissions of the beam switches.

A clearer understanding may be had of the physical structure of the beamswitches by reference to Fig. 8. This iigure shows the central cathode80o, the collector grid 80H and the annular series of anodes Bilt, tot,804, etc. As shown a in the Skellett Patent 2,217,774 referred toherein, the cathode llt@ may comprise a filamentary element locatedalong the central axis of the cylindrical envelope of the tube, and theanodes may comprise a series of vertically disposed cylindrical stripsarranged concentrically with respect to the cathode. The collector grid80E consists of a cylinder having a series of vertical slots miti, 006,807?, located in line with the central cathode and the respectiveanodes. The collector grid E is also provided with integral i'lns 00d,809, 8 l 0 which act as partitions to form spaces individual to therespective anodes. The purpose of these spaces between adjacent fins isto conne the secondary electron emission from the associated anodes toprevent interference between circuits connected to adjacent anodes. Inthe figure the primary emission from the central cathode 80() isillustrated by the electron beam 8| l, which in the constructiondescribed is in fact in the form of a sheet of electrons emerging fromthe illamentary through the slots in the collector grid, one after ktheother, as the beam rotates, and, as illustrated,

after passing through the slot 306 implnges upon The impingement of thebeam on the anode 803 causes the secondary emission of electrons whichare attracted back to the collector grid 80G by. reason of the potentialdiiference between the anode and the collector grid. As above noted andas illustrated in the figure, this secondary emission is confined to thespace formed by the fins 809 and. 8|0 and the anode 003. The beam switchshown in Fig. 8 is also provided with a control grid 8|2 the purpose ofwhich will be explained presently.

Inasmuch as the primary beam switch B may be paired with a plurality ofsecondary beam switches for concurrent conversations between a number ofpairs of lines, it is desirable. that the rotating beam of each of thesecondary switches shall remainvirtual in all of its angular positionsaround the cycle, except the position corresponding to the called line.In this position the virtual beam is transformed into a real beam inorder lill liti

This beam of electrons passes Y that conversation may take place betweenthe lines of the conversational pair. To ellect this transformation ofthe secondary switch beams these switches are provided with controlgrids 3i 0, 3l2, etc. The control grid 3|0, for example,

is biased negatively with respect to the cathode 305 by means of abiasing battery 320 which is connected to the grid through the coil ofhigh frequency transformer 32|. The normal bias on the grid 3l@ issuiiicient to prevent the iiow of electrons from the cathode 305 to theanodes in response to the voltage of battery 322. Therefore, as t1 yemagnetic held rotates about the switch 3mi, a virtual beam rotatestherewith until the position is reached occupied by the anode to whichthe called line is connected. At this same instant the rotating meam ilof the primary switch, which exists always as a real beam, is connecmdto the anode to which the calling line is connected. As the beam 2lirotates through its successive cycles it generates in the transmissioncircuits 201i, 205, etc., connected to the respective anodes, momentaryimpulses of high frequency, namely, a frequency which is one hundredtimes the frequency of the source Zit. When, therefore, the beam Eilengages the anode of one of the lines of a pair engaged in conversationthe high. frequency impulse developed in the associated transmissioncircuit (20d, for example) is passed by the high frequency transformer22l and is transmitted through the associated register fifi@ through thehigh frequency transformer @2i the control grid 3io. The polarity ofthis high frequency impulse is such. that it overcomes ino mentarily thenegative bias on the control grid 3l@ whereupon the beam 3l@ assumes areal character and electrons flow from the cathode 305i to the anode ofthe other line of said pair. An instant later, as the primary beam 2l?!moves on the Aanode of the first-mentioned line and passes to the nextsuccessive anode, the high frequency impulse ceases, the negative biasof the grid @I0 is restored, and the beam 3io resumes its virtualcharacter until it has completed another cycle.

A detailed description will now be given of the operation of the system,assuming that a plurality oi conversations are taking placeconcurrently. For this purpose it will be assumed that the subscriberof. line 20o (line No. 42) wishes to converse with the subscriber ofline 323 .(line No. 20) and that the subscriber of line 20! (line No.30) wishes to converse with the subscriber of line 32d (line No. 62).When the line ad@ calls, a starting condition is applied to conductor222, and, if the registers 300, 50o are the set next allotted for use,the controlling mechanism 402 of the finder register 400 starts theregister in operation to hunt for and seize the calling line 2te. Thenumber of the calling line being 42, the brush shaft 40E takes fourvertical steps and two rotary steps to bring the brush sets intoengagement with the terminals representing the calling line.Accordingly, the movable lcondenser plate 401 is rotated to its fourthposition relative to the stationary plates, and the movable plate 409 isrotated to its second position relative to the stationary plates. Whenthe register 400 reaches the terminals of the calling line, a testcircuit is closed over conductor 435, brush 43S, terminal 437 toconductor 438 on which a hunting condition exists. Closure of thiscircuitl causes the cessation of the hunting operation, and ground isthereupon applied over conductor 435 to render the line 200 busy toother registers. The loop of the subscribers line 200 is now extendedover conductors 439 and 440 through brushes 44| and 442, conductors 443and 444 to the operating mechanism Ell of the associated called lineregister 500. Ilhe calling subscriber manipulates his dial 223 totransmit the tens and units digits 2 and "0 of the called line 323.These impulses operate the register 500, which takes two vertical stepsand ten rotary steps to position the movable plates 503 and 505correspondingly. The shift of phase, which is negative in sense, imposedby the register 400 upon the voltage in the circuit 32 is equal to 4x36degrees +2 3.6 degrees or` -151.2 degrees; and the shift, which ispositive in sense, imposed by the register 500. upon the voltage incircuit 509 is equal to 2x36 degrees or +72 degrees. Therefore, theresultant shift, of phase of the voltage appearing in the circuit 509 is151.2 degrees +72 degrees or 79.2 degrees. Thus, as the beams 2H and 3iorotate in synchronism, each time the beam 2H reaches the anode 208,

which occupiesA a radial position 151.2 degrees' from the zero positionthe beam 3HE engages the anode 325 which occupies a radial position 72degrees from the zero position. In other words, the beam Si@ is laggingthe beam 2 il by the fixed angle 79.2 degrees, which is the phasedisplacement introduced by the phase-shifting registers 200 and 500 inaccordance with the numbers of the calling and called lines.

When the calling condition appears on the other calling line 201, thestart circuit is closed and the next available set of registers 600 andH00 is taken for use. The operating mechanism dit@ of the finderregister responds to the starting condition and operates the shaft 501three steps in a vertical direction and ten steps in the rotarydirection to drive the movable plate 600 to its third position relativeto the stationary plates and the movable plate E09 to its tenth position(a full cycle) relative to the stationary condenser plates. The settingof the register 200 on the terminals of the calling line 200 extends thecalling line loop over the conductors 225 and 22o and brushes dit andtit to the operating mechanism 707 of the called line register 200. Thecalling subscriber manipulates his dial 221 to transmit the tens andunits digits "6 and 2 of the called line 32d, and the register F00positions the movable plates E28 and '09 correspondingly. The negativephasel shift introduced by the setting oi the register dit@ is equal to3x36 degrees or -108 degrees, and the positive phase shift introduced bythe register lo@ is equal to 6x36 degrees +2 3.6 degrees or +2232degrees. Thus the resultant phase shift appearing in the circuit 'F05 is108 degrees +2232 degrees or 115.2 degrees. Thus, as the beams 232 and3W rotate in synchronism, each time the beam 2H reaches the anode 210,which occupies a radial position 108 degrees from the zero position, thebeam 3H engages the anode 32d, which occupies a radial position 223.2degrees from the zero position. In other words, the beam` 3 i l isleading the beam 2 i 'l by 115.2 degrees which is the phase displacementintroduced by the phase-shifting registers 600 and 180 in accordancewith the numbers of the calling and called lines.

The transmission circuits for conversation be`` tween the subscribers ofthe two pairs of lines will now be described. As above explained, thereal beam 2li of the primary switch is rotating in phase with and insynchronism with the voltage of the source 2id, the virtual beam 316 ofthe switch 300 is rotating Ain synchronism with but 79.2 degrees behindthe beam 2H, and the virtual beam of switch 30| is rotating insynchronism with but 115.2 degrees ahead of beam 2li. This relationcontinues as long as the subscribers remain in conversation. Assume thatat a given instant the primary beam 2l1 has reachedthe angular positioncorrespondingto the calling line 200 and is dwelling briefly on theanode 208. At this same instant the secondary beam 316 is dwelling onthe anode 325 individual to the called line 20. If at this instant thecalling subscriber' is speaking, the voice currents in the line `Zillithe common transmission medium 202. Also at this same instant the beam2W, upon striking the anode 202, has produced an impulse of highfrequency which is transmitted over conductor 202 through thetransmission circuit 20d and the high frequency transformer 22! thenceover conductors 230, brushes dit, conductors M6 to the primary windingof high frequency transformer 32E. This impulse is induced in thesecondary Winding ci the transformer 32i, and as above explained,opposes the normal bias on the control grid 3io, causing the beam 36S tostrike or to change trom its virtual to its real character.

Since at the instant assumed the common medium 322 has assumed a certainpotential, in accordance with the instantaneous value oi the callingsubscribers speech, the collector grid @uit likewise takes up acorresponding potential. Therefore, the real beam 3io is controlled inits intensity in a manner to produce a proportional potential on theanode 325 on whichit impinges. Theanode 325 being connected by Way ofconductor 32? to the transmission circuit 328 of the called line 20, thesuccessive potential values thus assumed by it in accordance with therotarI tion of the beam reproduce the audio-frequency Wave and causetalking current to now inthe subscribers line 323 representing thespeech of the calling subscriber.

Conversely, if the called subscriber is speaking 'at the instant thebeams 2i? and 3l@ are engaging the anodes representing the calling andcalled lines 2b@ and 323 respectively, the current variations in theline 323 cause potential variations to be applied by way of conductor32'i to the anode 325 on which the real beam @It is now impinging.'floevariations of potential on the anode 325 cause through thesecondary electron emission corresponding variations on the collectorgrid 303 at the successive instances marked by the striking of the beam,and this succession of diiiering potentials are applied over the commonmedium 202 to the collector grid 292 of the beam switch 205. Theappropriate succession of potentials of the collector grid 2&2 vary atthecorresponding instances the intensity of the beam 2li, resulting in`a succession of diiering potentials on the anode 208 which reconstructthe audio-frequency wave shape. The resulting voice variations areimparted over conductor 2011 to the transmission circuit 20d and areinduced through thetransformer 228, causing the flow of talking currentin the calling subscribers line 2o0.

dit, a fragment of the speech is transferred in this manner between thecalling and called lines For each of the rapidly recurring cycles of thebeams 2H and 200 and 328, the fragments following so rapidly upon eachother as to give the impression of continuity to the speakers inaccordance with the principles of the time division form of multiplextelephone system.

In a similar manner the synchronous beams '2H and 3H engage the anodes2|0 and 3 26 simultaneously and repeatedly; at each such engagement ahigh frequency impulse is transmitted by way of transmission circuit205, high frequency transformer 23|, circuit 232, brushes 6i2, circuitSIB, causing the beam 3H to strike; and transmission takes place ineither direction between the calling line 20| and the called line 324.

When the subscribers have ilnished their conversation they replace theirreceivers on the switchhooks, and the calling condition is removed fromthe line circuits 202 and 203, permitting the release in any well-knownmanner of the register sets 400, 500 and 600, lull. These registers maynow be selected in response to new calls on any oi the subscribers'lines.

Thus it will be appreciated that the speech of each individualconversation is transmitted through this system, over the commonconnecting medium of it, as a rapid succession of sharp impulses, thesuccessive peak values of any one set of which trace out 'thevoice-frequency wave oi. that particular connection. It is this featurewhich enables the single rotating beam switch i@ (Fig. l) to accommodatesimultaneously calls over all of the lines associated with it. This itdoes by transmitting for each such line over the common medium for but abrief interval in accordance with the superposition principle of thetime-division multiplex type of system. In that type of system two suchrotating switches are employed, one at each end, which are operated insynchronism and in iixed phase relation, whereby a given line at one endis always connected with a given line at the other, and generally in thesamerelative position. The departure from this prior art in the presentsystem, in respect to this time-division multiplex phase of it, is thatthe present system provides for connecting any one line at one end ofthe system with any other line at the other end.

It has already been explained thatI the invention contemplates the useof virtual as well as real beams of electrons. The controlling eld whichrotates the radial beam may be electrostatic instead of electromagneticas illustrated. The inventionalso contemplates the use of beams of otherforms of energy, and it should be understood that whenever thespecication or claims speak of these beams either in motion or in theirinstantaneous positions these descriptions are intended to apply to thebeams in their virtual nature as well as in their real form.

It Awill be understood that other types of phase shifters may be used ifdesired. For example the rotating condenser plate may be replaced by asuccession of xed networksccmprising tapped condenser units which areconnected to sets of contacts selected by the settings of the registerswitches.

What is claimed is:

l. The combination in a communication system of a group of lines, meansfor causing a beam of energy to scan said group of lines repeatedly andto establish communicative engagement with any desired line in saidgroup, means for causing a second beam of energy to scan said group andto establish communicative engagement with any transformer 329 to thecontrol grid SI2,

desired line in said group, and means for controlling the relationbetween said beams to establish communicative engagement simultaneouslybetween any desired pair of lines in said group.

2. The combination of a communication system of a group of elements,means for producing two separate beams of energy, means for driving saidbeams synchronously to traverse the elements of said group repeatedly,circuit means including said beams in serial relation for establishingcommunication channels between elements of said group, and means forvarying the phase relation between said beams for causing them totraverse any desired pair of elements simultaneously and repeatedly toestablish a connection between said pair of elements.

3. The combination in a signaling system of a group of lines, each linehaving a different designation, means for producing two separate beamsof energy, means for driving said beams synchronously to traverse thelines of said group repeatedly, circuit means including said beams forestablishing signaling channels between pairs or lines of said group,and means controlled in accordance with the designation of one of thelines of any desired pair to determine the phase relation of said beamsfor causing them to engage the lines of said pair simultaneously andrepeatedly to es tablish a connection between said pair of lines.

4. The combination in a signaling system of a group of lines, each linehaving a different designation, means for producing two' separate beamsof energy, means for driving said beams synchronously to traverse thelines of said group repeatedly, circuit means including said beams forestablishing signaling channels between pairs of lines of said group,and means dependent on the designations of both lines of any desiredpair for adjusting the space relation of said beams to cause them toengage the lines of said pair simultaneously and repeatedly to establisha connection between said pair of lines.

5. The combination in a signaling system of a group of lines havingappearances arranged in a fixed spatial relation, each of said lineshaving a definite designation, means for producing two movable beams andfor driving them synchronously and cyclically over said fixed lineappearances, circuit means including said beams for establishingsignaling channels between the lines of said group, and means foreffecting a time displacement between said beams corresponding to thespatial displacement between any desired pair of lines in said group.

6. The combination in a signaling system of e group of lines havingindividual appearances arranged in a xed spatial relation, each of saidlines having a diierent designation, means for producing two movablebeams and for driving them synchronously and cyclically over said xedline appearances, means including said beams for establishing signalingchannels betweenI the lines of said group, and means dependent on thedesignations of the lines of any desired pair for ei'- fecting a timedisplacement between said beams corresponding to the spatialdisplacement between said pair of lines.

7. The combination in a communication system of a group of lines havingappearances arranged in a xed spatial relation, each of said lineshaving a different designation number. means' for producing two beams ofenergy and in synchronism over the xed appearances of said lines,registers for registering the ,designations of any desired pair o:

lines, and means controlled by said registers for effecting atime'displacement between said beams oi energy corresponding to thespatial displacement between the lines of said pair to cause said beamsto engagethe lines of said pair simultaneously.

8. The me'thod of establishing a signaling connection between any pairof lines of a group of lines which comprises arranging said lines in axed spatial order, causing beams of energy to traverse said linessynchronously and cyclically, and eilecting a phase displacement betweensaid beams of energy corresponding to the spatial displacement of thelines oi the desired pair.

9. The method of establishing a signaling connection between any pair oflines cfa group of lines which comprises arranging said lines in a nxedspatial order, causing beams of energy to traverse said linessynchronously and cyclically, and utilizing the designations of saidlines for eifecting a phase displacement between said beams of energycorresponding to the spatial displacenient of the lines of the desiredpair.

10. The combination in a Signaling system of a group of elementsarranged in xed spatial relation, means for producing a plurality ofbeams .of energy and for driving them synchronously and cyclically oversaid xed elements, means including said beams for establishing signalingconnections between said elements, means for introducing phasedisplacements between said beams for causing them to engage theelementsof a plurality of pairs, each pair comprising any element andany desired other element, the engagement o! the' several 'pairsoccurring cyclically and sequentially and the engagement of the elementof cach pair .occurring simultaneously., v

i1. The combination in a communication sus tem of a group of lines, aprimary beam switch in which said lines appear in a xed spatialrelation, a secondary beam switch in which said lines appear in the sameiixed spatial relation, means tor driving the beams of said switches insynchronism to scan said lines successiveh' and cyclically, meansincluding said beams for establishing communication connections withsaid lines, and'means for introducing phase displace# ments between saidbeams forcausing them to engage the lines of any desired pair simultaneously. y

12. The combination in avcommunication sys= tem of a group oi lines, twobeam-producing de-a vices, said lines appearing in a lined spatial rela@tion in both of said devices, a source of voltage of a given frequency.circuit means for applying voltage from said source to said devices todrive both beams at synchronous speed over said tem of a group of lineshaving designationsbased on the decimal system., means for producing`beams of energy, a source of voltage for driving said beamssynchronously tov scan the lines o! said group, a pair oi phase-shittingregisters for registering the digital values of the vdigits in twosuccessive digital places of the designation of any particular one ofsaidv lines, means for setting said registers in accordance with thevalues of the, correspondingc digits of said particular line, cir-A cuitmeans for applying voltage from, said source to said registers in seriesto eiect a shiit'ot phase which is the sum oi the shifts produced bysaid registers. each register serving to shift'the phase yby an amountproportional to the numerical value of the digit registered thereon. andmeans for changing the frequency-oi the voltage applied to one of saidregisters with respect to the irequency applied to the othe yregister byan amount which corresponds 4to the dierence in decimal value betweenthe successive decimal places to which said registers correspond.

l5. The combination in a communication system of a group oi lines havingdesignations based on the decimal system, meam -for producing beams ofenergy, asource of voltage for driving said. beams synchronously to scanthe lines' of said group, a pair of phase-shifting registers forregistering the digital values of the digits in two successive digiiziplaces of the designation oi any particular one of said lines, means forsetting said registers in accordance with the `values of thecorresponding' digits of said particular line, circuit means forapplying voltage from said source tosaid registersinseriestoeiiect ashift ofphuow isthesum ofthe ahiftsproduced by am s ri-rie: servingtoshift the phase b w propomonai to the numerical value oi the digittheln.

lines in succession and cyclically, and phaseshifting means for shiftingthe phase of the voltage applied to one of said devices to'introduce adesired phase displacement between said beamse 13. The combination in acommunication sys= tem of a group of lines arranged in ilxedspatialrelation, means for producing two separate beams oi energy,l means fordriving said beams synchro-= nously to traverse the lines of said grouprepeatedly. circuit means including said beams for establishingcommunication connections between said lines, and phase Shifters forshifting theA phase of one of said beams in opposite senses to introducea. resultant shift in the phase ot said beam relative to the phase ofthe other beam which corresponds to the spatial displacement of anydesired pair of lines in said group.

i4. The combination in a communication sysmeansfor multiplying` thefrequency of the volt-I age applied to a particular one'oi saidregisters by a factor representing the dinerence in decimal valuebetween the digital place to which said reg ister corresponds and thedigital place to which. the other oi said registers corresponds, andmeans for dividing by the same factor the frequency ot the voltage afterit has experienced the shift of phase imposed by said Aparticularregister and before it is applied to said other phase-shiftingregister.l

16. The combination in a communication system of a. plurality of lines.a common medium having communication channels,F one between each lineoi' said plurality of lines and each other line oi' said plurality. beamswitches in which the channels or said common medimn appear, means fordriving the beams of said switches synchronously over said channelappearances, and means y controlled by any particular one of said linesfor shifting-the phase relation between said beams to select thecommunication channel of said cnmon medium which interconnects saidparticular line and any other desired one of said lines.

1'1. The combination in a communication system of a plurality o! lines,a common medium having communication channels, one between each line o!said plurality voi lines and each other line ot said plurality. beamswitches in which the channels ot said common medium appear, means fordriving the beams of said switches synchronously over said channelappearances, and means controlled by any number or said lines as callinglines' for varying the phaserelation between said synchronousbeams toselect the communication channels which interconnect said calling linesrespectively with e. corresponding number of said lines chosen at willas called lines for concurrent communication. r

18. The method of interconnecting any pair of lines of. a plurality oflines over a. common transmission medium which consists in establishingin said medium recurrently and in rapid succession time-separatedtransmission channels individual respectively to said lines and shiftingthe position of any one of said channels in time to coincide withthetime position of any other one of said channels.

osmosi 19. The method of interconnectingany pair of stations of aplurality of stations over a common transmission medium which consistsin establishing in said medium recurrently and in rapid successiontime-spaced transmission channels individual respectively to saidstations, and shift;

ing the position of any one of said channels in time to coincide withthe time position of. any other one of said channels.

LLGYD ESPENSCHIED.

